Conventionally, due to the features such as the possibility of high-speed heating and easiness in temperature control, a high-frequency induction heating apparatus has been used to heat various objects to be heated.
In the field of production of a can body, a technology in which a thermoplastic synthetic resin film (e.g. a polyester film or the like) (hereinafter, appropriately abbreviated as a film label) which has been subjected to gravure printing or the like in advance is attached to a molded can trunk to produce a 2-piece can body has been put into practical use. This technology has a can body heating process in which a can body is heated by a high-frequency induction heating apparatus.
For example, Patent Document 1 discloses a technology of an apparatus for producing a film label-attached 2-piece can body (also called a film label-attaching apparatus) characterized in that, in an apparatus for producing a film label-attached 2-piece can body in which a 2-piece can body of which the trunk has been molded is fitted to a mandrel, and a film label is attached to the outer circumference of the trunk during the conveyance of the can body, the apparatus is provided with a heating means that heats a can body to a predetermined temperature along the revolution path of the mandrel and a cooling means that cools the film label-attached can body subsequent to an attachment roll. In this technology, a high-frequency inducting heating coil is used as the heating means of a can body.
Patent Document 2 discloses a technology of a film-attaching apparatus (also called as a “film label-attaching apparatus”) in which a decorative film is attached to a can body similar to that in Patent Document 1.
This technology is characterized in that, in addition to the can body-heating means, a mandrel-heating means that inductively heats an outer sheath element of a mandrel is provided. In both of these means, a high-frequency induction heating coil is used. FIG. 5 of Patent Document 2 shows a schematic oblique view of the shape of the high-frequency induction heating coil.
Further, various technologies regarding a high-frequency inducting heating apparatus have been proposed.
For example, Patent Document 3 discloses a technology of a high-frequency heating apparatus that inductively heats parts to be heated of a metal body, which comprises a plurality of heating coils helically formed and arranged and fixed with a predetermined interval being provided with each other and a conveyance means that conveys the metal body such that the parts to be heated are passed sequentially above each heating coil, wherein the parts to be heated are sequentially subjected to high frequency heating by an induction magnetic field of each heating coil. The heating coils are connected in series or in parallel.
Further, Patent Document 4 discloses a technology of an induction heating apparatus in which a plurality of heating coils are connected in parallel to one high-frequency power source, and AC reactors are respectively connected in series in correspondence with each heating coil.
Patent Document 5 discloses a technology of an electromagnetic heating apparatus provided with a resonant circuit having an induction heating coil for heating an object to be heated and a switching circuit for supplying high-frequency current to the resonant circuit, in which the induction heating coil is provided with a plurality of first coils connected with each other in parallel and second coils that are respectively connected to the first coil in series, the coils are arranged approximately concentrically on an approximate same plane, the resonant circuit is divided into the number of the pair of the first coil and the second coil, and, according to the resonant circuit, an independent switching circuit is connected.